We did this exact thing last year in early June. Answers about what to do to get in line for your PPO rides on 7DMT and PPF here: BOG breakfast on an EMM day
I don’t have answers about the bus, as we always stay offsite.
As for timing, get in line at the far left turnstiles by 7:45 am at the latest or earlier if you can, especially if you want time to take photos of the castle and “wander” a little prior to your reservation. The EMM crowd and PPO ADR crowd get in the same entrance line, which is pretty obvious. They will hand you a map to tell you what route to take to get back to your ADR. It takes you through around the left of the castle, if they haven’t changed it yet.
You’ll be cutting it close with an 8:10 reservation if you plan to take it slow to get back there, even if you pre-order online beforehand (which is HIGHLY recommended). Although every PPO ADR is able to get in at 7:45-7:50 with all the EMM people, you still have to get there by reservation time.
As others have said, the ability to “wander” is there, but it’s a pretty restricted space. I would leave that until after you finish breakfast. After you are done, you can come “wander” around and then get in one of the designated lines for the PPO ADR crowd for either 7DMT or PPF, using the instructions from the other post.